Detector circuit



Dec. 27, 1938. l.. E. BARTON DETECTOR CIRCUIT Filed May 8, 1937 TH T 3mA u .wu

Patented Dec. 27, 19.38v

Egli-LESS UNITED s TArEs PATENT oEEicE DETECTOR CIRCUIT'v Loy E.,Barton,Collingswood, N. J.,assignorV to Philco Radio and TelevisionCorporation, Philadelphia, Pa., a corporation fofDelaware' ApplicationMay 8, 1937, `Serial No. 7,141,561

v 12 claims. (111.250,-20)

`'Ihis invention relatesto arnovel detectorrcir- -.cuit for a radioreceiver or the likeembodying .gart. The present invention is directedspecifical- 1y to the .detectorjsystem comprising lthe trans- -formerfT,thedetectorf tube D, and the associated. 5 circuits. Thedetectorsystem-may be .coupled to" thelast stage ofthe intermediatefrequency amy-plier .or;to a driver tube, `as represented by the:automatic volume control and is useful, forexample, in asuperheterodyne radio receiver. More 5wspecical1y, the invention relatesto radio-receiv- 'ing'.systems. in which it is desired .to obtain bothan*V audio signal Vand an automaticvolumecontrol signal from thedetector circuit, and .in which it is desired to obtain the-automaticvolume conf -lO ltrol signal from a primary circuitY and to obtain -theaudio signal from a secondary circuitasso- *ciated with the primarycircuit. i

One obj ect of the invention is to provide a` circuit of this classWhose selectivity orresponse v4l5 characteristic is decidedlybetter'xthan -those of .prior devices, particularly in that theYselectivity Icharacteristic curve has ak flat Yblunt nose land steepSides, thus giving higher fidelity and better adjacent channelattenuation than ,prior devices ofthe same general class.

Another object of the invention is to provide 1;

n a-device Vof this character wherein the response Y characteristic ofthe automatic Volume control system is broader than that of theydetectorcircuit so that the automatic volume control system rbecomesoperative before anoutput signal is ob-v tained as the receiver is tunedto a-desiredstation.

' A further object of the invention is .to Iprovide I :lo a device ofthe stated character `wherein the selec- Vtivity characteristic of thedetector circuit is symmetrical with respect to the carrier frequency.

' A still-further object of :the invention is to provide afdetectorcircuit of the type specied which may employ a'conventionaldoublediodetriode vacuum tube' and in which the deleterious yeffectsoithe inherent interelectrode capacities in a tube of this type may bealleviated.

YThe inventionmay be more clearly understood .1?) -by referenceto theaccompanying drawing in which there are illustrated a preferred .form ofthe-invention and certain'characteristics thereof.

`In the-drawing: Fig. 1 is a diagrammatic illustration of a supertion; f

' Fig. 2 is a graph illustrating certain character- 'y istics'of-theinvention; and

Fig. 3'illustrates a specific form of the transthe terminals ra and dthereof. 50

.3o former employed'inthe detector circuit.

Referring to Fig. 1, there. is shown a typical `voltage which is builtup across resistor R1 by radio receiver of 'the superheterodyne typewhich,

heterodyne radio receiver embodying-the invencomprising resistors R andR1 and the radio fresince the construction and operation of Isuch a:receiver is well understood by those skilled-.in the tube" V. 5- y'Iv'heprimary winding P yand lthe secondary;10 winding S ofthetransformer TareV tappedat in- ;termediatepoints/b. and' e,respectively,... each of Which-points should preferably be at theelectrical centerV or :midpoint ofthe particular winding.

4the output electro-de or .anode of the tube V.'Ihlmidpointofftheprimary Winding is also con- .wnected tofgroundthrough a path having low im- 20 pedance at radio frequency, which-pathmay consistof a separate connection to ground through a blockingcondenser, as il1ustrated,.or may comvv`prise a suitable fllterinvthe'energy supply circuit Vfor the tube V. The entire primary Windingis 25 tuned torthecarrierrfrequency by means of a condenser connectedthereacross, as `well understood.

The center-tapped secondary .winding S, which is electromagnetically.coupled to the primary Winding-is also tuned to the carrier frequencyby` means of afcondenser connected across the Winding, as illustrated.The-extremity or terminal d -of:.the.. secondary -windingis connected tothe anode Vof `the diode .d1 of the detector tube D. 35

The anode-of the other diode d2 of the detector' tube is connected tothe terminal a of the primary 'winding through .the small blockingcondenser C1.

It will bev understood, of course, vthat this connection to the primarywinding, as well as the` connection of the anode of tube V to theprimary winding,imay be made to a tappedpointnear the Y endoi theprimary windinginstead of at an end thereof. The midpoint e of thesecondary Vwinding -is connected to the diode circuit or audio loadquency by-pass condensers C. The primary and secondarywindings arepreferably polarized so asv to minimize the potential difference betweend1, is supplied to the rgrid-cathode or input circuit. ofthe triodeportion of tube D through cone.

denser C2, potentiometer P and condenser C3. A suitable bias may besupplied toI the grid of tube D through the grid-leak resistance R2. Theamplified audio signal from tube D is supplied to the usual audioamplifier, as illustrated.

The anodel'of the diode d2, which may be-termed the A. V. C. (automaticvolume control) diode, is connected to the automaticjvolumecontrolcircuit comprising the resistors R3 and R4 ,and bypass Vcondenser C4,which circuit is connected to a portion of the radio receiver ahead ofthe tube V. 1-

in a manner to control the amplification or gain of the system. Sinceautomatic volume control systems are now well understood, this circuitrequires no detailed explanation. The connection of the circuit to theportion of the radio receiver to be controlled may be made in accordancewith any of the conventional methods and practices. If desired, a delayvoltage may be appliedto the automatic volume control system through theresistance R4. Y' A Y From the above description, it vwill be seen thatthe incoming modulated carrier signal is supplied to the portion of theprimary winding P between the points a and b and is thus transferred tothe circuit of diode d1 comprising the portion of the secondary Sbetween the points Vd and e. The audio signal derivedby therectification action of the diode dr is supplied to the triode amplierportion of tube D, as aboveV described.Y At the same time, a portionofthe signal energyfrom tube V is supplied to the diode d2, the loadcircuit of which includes the resistor R4. The voltage built up acrossthis resistor is utilized for the purpose of automatic volume control asabove mentioned.

It has been found that in a circuit of this character, the capacitybetween the anodes of the diodes d1 and d2 and the stray capacitybetween the leads Vconnected thereto, introduce a fortuitous capacitycoupling between the primaryV winding P and the secondary winding S, asvindicated at C5.

' several micro-nuorofarads and tends'to disturb the selectivityVcharacteristic ofthe transformer T, causing it to becomenon-symmetrical. A typical illustration of the non-symmetricalselectivity characteristic curve which is thus produced is shown at A inFig. 2, 'wherein the abscissa represents the frequency of the testsignaland the ordinate represents on a logarithmic `scale the amplitude of theinput signal required to produce a standard output signal.

v be obtained, for example, using the circuit of Fig.

l, by connecting la `signal 'generator to the grid of tube V anddetermining the amplitude and frequency of a signal from the signalgenerator required to produce a certain d c. voltage across the loadresistance in the circuitof the audio diode d1. For example, amicro-ammeter might be connected in the circuitV of diode d1 and theoutput of the signal generator Vadjusted so asto produce a certainreading of the micro-ammeter. It has been found further that increasingVthe capacity between the anodes of the diodes d1 and d2 tends to makethe characteristic curve more non-symmetrical; Y

In accordance with the present invention, this eiect is reduced byintroducing a capacitance Ce between Vthe opposite extremities orterminals,

c and f of the primary and secondary windings.

It is found that as this capacitance is increased,

the response or selectivity characteristic becomes more symmetrical `andthere-is finally produced the symmetricalV curVe'B of Fig. 2. If thecapac- Such capacitance may amount to Such curve might Y ity isincreased further beyond the value giving the symmetrical curve, thecurve again becomes non-symmetrical but on the Vopposite side of theaxis as illustrated by the curve E in Fig. v2. It has been found ythatwhere both the primary and secondary windings are center-tapped, thecapacitance Ca should be substantially equal'to the fortuitous.capacitance C5.Y Ihe position of the tapped points b and e may bevaried; however, under these circumstances the Ycapacitance C6 will havea value different from that of the for-- tuitous capacitance C5.

VIn addition to the advantage above noted, the circuit of the inventionmaterially improves the shape of the selectivity characteristic as maybe seen from Fig. 2. As compared with a characteristic curve obtained byusing two tuned circuits coupledl tothe same degree and otherwisecomparable, it is found that the symmetrical curve B produced by thecircuit of the invention is flatter over the `useful operating rangeand, therefore, the circuit gives better fidelity; and, furthermore, thesides. of the curve B aresomewhat steeper, thus improving theadjacent'channel attenuation. Both of these features, viz. Ythe flatblunt nose andthe steepsides of the curve B,

' rived from theV primary circuit.A It will be noted also that theselectivity of the automatic volume control circuit is broader than thatof the detector circuit, as a result Yof which the gain of the radioreceiver is reduced before theaudio signal builds up to its vnormalvalue .as the receiverris tuned to a strong station. Consequently,momentary blasting of the receiver, which mightotherwise occur in Ytheinterim during which the A` V. C.

voltage is building up, is effectively avoided.

A further feature of the invention resides in thefact that by connectingthe input and output circuits of the transformer T to taps on theprimary and secondary windings, theY impedance presented by thetransformer to the tube V and to the diodes d1 and dz'may be reduced toa certain extent, thus permitting more eicient matching between theseveral circuit elements without requiring the use of non-standardparts.

- In Fig. 3, there is illustrated Va speciflcform of the transformer Tby the use of which satisfactory results have been obtained. VIn thisinstance,` the primary and secondary windings each comprisestwopie-wound sections or coils each comprising 110 turns of 7-41litzendraht wire universallyl wound in the 'same direction on a tube Gone-half inch in diameter. In each case, the total inductance of the twosections or coils was 1290 micro-henries, and the condenser employedwith each of them was of suflicient value to tune the circuittoresonance at a vfrequency of 465 kilocycles. VThe capacity of eachpadding ycondenser was approximately 100 "micro-microfarads. The mutualinductance betweenV the primary and secondary windings was 53microhenries which, in combination with the capaci- Ycuits. TheV twosections of the primary windingyas well as those of thesecondarywinding,

were* spaced apartwabout ione-sixteenth .of an inch, and a comminutediron core was used with each winding lor coil as shown at H and I, re-

'and tap points of thewindingsare clearly identified. Theconnectionsbetween the two pies was usedV as'theicenter tap'; 'Y Theentire transformer wasfmountedi in a conventional cylindrical housingone and three-fourth inches in diameter.

In thespeciiic device mentioned, a type 'l5 detector tube was employed,and the several components ofthe A. V. C. and audio load circuits weregiven conventional values- .A type .'78 tube was used for-V andbothtubes .were operated at their ratedvoltages The coupling capacity Ci'and the kcapacity C6 were Ybuilt into the padding vcondenser itself,.the capacity C1 being obtained `by adding 'an additional plateto thepadding condenser, while the capacity Cs was obtained by the properspacingand proximity of the sol- Cil points on said windings,

dering lugs on the condenser. .e In. addition tothe. above, thefollowing values were assigned to 'certainr of the elements:

' C1=110 micro-microfarads R,=,`100,000 ohms C 110 micro-'microfaradsR1=1/3 `meshm P 1 megohm R2`=1.5jmegohms C4 `:0.15 microfarad R3=1megohm R4=% megohm l C5=C6=2 micro-microfarads It will be understood, ofcourse, that the in- -vention is not limited-tothe specific embodimentillustrated and described herein nor to the values cf the variouselements given as aspecific eX- ample. The invention is capable ofVvarious embodiments or modifications which may be resorted to withoutdeparting from its scope.

I claim:

1. In a signaling system, a transformer having a primary winding and asecondary winding, means for tuning said windings `Ato a desiredfrequency, means for supplying signal energy to part cf said primarywinding, a diode rectifier connected across part of said secondaryVwinding so as to receive signal energy therefrom,` means for derivingrectified signal from the circuit of said rectifier, a second dioderectifierconnected to said primary winding, there being a fortuitouscapacity coupling introduced between said windings bysaid dioderectifiers, means providing a low impedance rpath between intermediatecapacitive coupling means between said windings for reducing` theleffect of said fortuitous coupling,'and means for deriving rectifiedsignal fromsiaid second diode rectifier,

2. In a signaling system, a transformer having a primary winding and asecondary winding, means for tuning said windings to a desiredfrequency, means for supplying signal energy to said primary winding, adiode rectifier connected in circuit with a Dart of said secondarywinding so as to receive signal energy therefrom, means foi` derivingrectified signal from the circuit of said rectifier, a second dioderectifier connected ,tofaipart -of-said primary winding, there being a-fortuitousfcapacity coupling introduced between said windings by Vsaiddiode rectiers, means providing a low impedance path betweenintermediate pointsA of said windings, capacitive coupling -meansbetween ysaid windings for reducing the effect..of.said fortuitous.coupling, and means for y.derivingrectified signal from said seconddiode rectifier.

3,. In a signaling system, a transformer having a primary l.winding and.a secondary winding, ymeansforttuning saidv windings to a desiredfrequency, means Vfor supplying signal energy to part of said.primary-.winding a diode rectifier connected in circuit with a part ofsaid secondary winding. soas toi receive signal energy therefrom,.avloadimpedance in circuit with said diode .rectier for deriving a rectifiedoutput signal therefrom,..a secondv diode rectifier connected to a partof said primary winding, there being a forltuitous capacity couplingintroduced between said.

windings by said diode rectifiers, means providing a lowimpedance pathbetween intermediate points of'said-windings, capacitive.V couplingmeans between 'saidwindings for reducing the eect of vsaid'fortuitous4coupling, and ra load impedance in circuit with saidsecond dioderectifier for deriving' a rectified signal therefrom.

:4. In a signaling system, a transformer having a .primary .winding anda secondary winding, means forv tuningsaid windings lto a desiredfrequency, vmeans for..supplying signal energy to part of said-.primarywinding, a diode rectifier connected. in circuiti with a part of saidsecondary winding so as to receive signal energy therefrom, a. loadvimpedance in circuit with said diode rectifier kfor deriving-LaVfrectied output signal therefrom, a' second diode rectifier connectedto ari'part of .said primary winding, said windings beingpola1ized'to.minimize the potential between .theV parts of said windingsto which said .diode rectifiers are connected, there being afortitouscapacity coupling introduced between said windings by saiddioderectifiers, means providy ing alow impedance-path 'between intermediatepoints of said windings, capacitive coupling means between said windingsfor reducing the effectv of saidfortuitous coupling, and a loadimpedance in circuit with said second diode rectifier for deriving a-rectied signal therefrom.

5. In a signaling system, a transformer having a primary winding and asecondary winding, means for tuning saidy windings to a desired fre-Yquenc'y', lmeans` for supplying signal energy to said `primary winding,a vacuum tube including two 'diodes in `tliesame-erivelope, meansconnecting one of the diode rectiers of said tube in' circuit Awith apart of said secondary winding so as to receive signal'energy therefrom,a load impedancev iri circuit with said diode rectier forderiving arectified' output signal therefrom,

means'. connectin'g'the other diode rectifier of from said other dioderectier, and means for utilizing said last-named signal to control theamplitude level of the signals transferred by said system.

6. In a signaling system, a transformer having a primary winding and asecondarywinding, means for tuning said windings to a desired frequency,a source of signals connected between an extremity and an intermediatepoint of said primary winding, a vacuum tube including two dioderectiers in the same envelope, means connecting one of the diode anodesof said tube to an extremity of said secondary winding', means includinga load impedance connecting an intermediate point of said secondarywinding to the cathode of said tube, means for deriving aY rectifiedsignal from said load impedance, means connecting the other diode anodeof said tube to the said extremity of said primary winding, there beinga fortuitous capacity coupling introduced between said windings by saiddiode ancdes,'means providing a low impedance path between the saidintermediate points of said windings, Ycapacitive coupling means betweenthe other extremities of said windings for reducing the effect of saidfortuitous coupling, and means for deriving a rectified signal from`said other diode rectifier.

7. In a signaling system, a transformer having a primary winding and asecondary winding, means for tuning said windings to a desiredfrequency, a source of signals connected between an extremity and anintermediate point of said primary winding, a vacuum tube including twodiode rectiers in the same envelope, means connecting one of the diodeanodes of said tube to an extremity of said secondary winding, meansincluding a load impedance connecting an intermediate point of saidsecondary winding to the cathode of said tube, means for deriving arectied signal from said load impedance, means connecting the otherdiode anode of said tube to the said extremity of said primary winding,there being a fortuitous capacity coupling introduced between saidwindings by said diode anodes, means providing a low impedance pathbetween the said intermediate points of said windings, capacitivecouplingmeans between the other extremities of said windings forreducing the effect of said fortuitous coupling, and means for derivinga rectified signal from said other diode rectifier, and means forutilizing said lastnamed signal to control the amplitude level of thesignals transferred by said system. v

8. In a signaling system, a transformer having a primary winding and asecondary winding,Y

means for supplying signal energy to a part of said primary winding, aspace discharge device having a plurality of electrodes, one of saidelectrodes being connected to a part ofsaid secondary winding so as toreceive signal energy therefrom, another of said electrodes beingconnected to a part of said primary winding, there being a fortuitouscapacity coupling introduced between said windings by said electrodes,means providing a low impedance path between intermediate points of saidwindings, and capacitive coupling means between said windings forreducing the eifect of said fortuitous coupling.

9. In a signaling system, a transformer having a primary winding and asecondary winding, means for supplying signal energy to a part of saidprimary winding, a space discharge device having a diode rectifier andat least one additional element, means connecting said element incircuit with a part of said secondary winding so as to receive signalenergy therefrom, said diode rectifier being connected to a part of saidprimary winding, there being a fortuitous capacity coupling introducedbetween said windings by the interelectrode capacitance of said dioderectifier and said element, means for providing a low impedanceV pathbetween intermediate points of said windings, capacitive couplingbetween said windings for reducing the eifect of said fortuitouscoupling, means for deriving a rectified signal from said dioderectifier, and means for utilizing said rectified signal to control theamplitude level of the signals transferred by the said system.

10. Ina signaling system, a transformer having a primary winding and asecondary winding, means for tuning said primary winding to a desiredfrequency, means for tuning said secondary winding to said frequency, asource of signal energy connected between an extremity of said primarywinding and an intermediate point thereof, means for deriving a signalfrom a portion of said secondary winding between an extremity of thesecondary winding and an intermediate point thereof, means providing alow impedance path between the said intermediate points of saidwindings, a capacitive connection between the said extremities of saidwindings, and capacitive coupling means between the other extremities ofsaid windings.

ll; In a signaling system, a transformer having a primary winding and asecondary winding, means for tuning said primary winding to a desiredfrequency, means for tuning said secondary winding to said frequency, asource of signal energy connected between kan extremity of said primarywinding and an intermediate point thereof, .a load circuit connectedbetween an extremity of the secondary winding and an intermediate pointthereof, means for deriving a signal from said load circuit, meansproviding a low impedance path between the said vintermediate points ofsaid windings, a capacitive connection between the said extremities ofsaid windings, and capacitive coupling means between the otherextremities of said windings.

12. In a signaling system, a ing a primary winding and a secondarywinding, means for tuning said primary winding to a desired frequency,means for tuning said secondary winding to said frequency, a source ofsignal energy connected between an extremity of said primary winding andan intermediate point thereof, a load circuit including a dioderectifier connected between an extremity of the secondary winding and anintermediate point thereof, means for deriving a rectified signal fromsaid load circuit, means providing a low impedance path between the saidintermediate points of said windings, a capacitive connection betweenthe said extremities of said windings, and capacitive coupling meansbetween the other extremities of said windings.

yLOY E. BARTON.

transformer havi

